This invention is directed to eddy current probes for internal or external inspection of tubes or other cylindrical components, and in particular, to probes for providing defect signals which may be distinguished from noise signals.
Conventional bobbins or encircling probes are normally effective in inspecting cylindrical or tubular components. Examples of these are U.S. Pat. No. 2,855,564, which issued on Oct. 7, 1958, to E. M. Irvin et al; U.S. Pat. No. 3,952,315, which issued on Apr. 20, 1976, to V. S. Cecco; U.S. Pat. No. 4,079,312, which issued on Mar. 14, 1978, to M. L. Osborn et al; U.S. Pat. No. 4,083,002, which issued on Apr. 4, 1978, to J. J. Allport.
In order to be able to internally inspect components, such as heat exchanger tubes, for internal defects in the presence of probe wobble or internal tube variation, such as tube distortion created by the `pilger` tube reduction process, a probe which will produce a defect signal that is different than a noise signal, is needed. U.S. Pat. No. 3,197,693, which issued on July 27, 1965, to H. L. Libby, and U.S. Pat. No. 3,753,096, which issued on Aug. 14, 1973, to W. C. Wiers, are examples of probes in which attempts are made to compensate for the noise problem caused by lift-off. U.S. patent application Ser. No. 283,092, filed by H. W. Ghent et al on July 13, 1981, which corresponds to Canadian patent application No. 359,392, filed on Aug. 18, 1980, describes an eddy current surface probe which provides different defect and noise signals when the probe is used to test surfaces. These probes cannot be readily applied to the internal or external inspection of tubes or cylindrical components.